A semiconductor module in which a power semiconductor element such as an insulated gate bipolar transistor (IGBT) is built into an outer case made from a resin is known as an example of a semiconductor device that controls a motor or the like. A semiconductor module including a control circuit board that controls a power semiconductor element is also known. In a power semiconductor module that includes a control circuit board, noise generated during a switching operation of a power semiconductor element may have an influence on the control circuit board and the power semiconductor element. Thus, the control circuit board is fixed to the outer case to be separated from the power semiconductor element such that the influence of noise does not reach. The control circuit board is fixed to an outer side of the outer case with screws, for example.
Higher operating speed, smaller size, and lower power consumption required for recent electronic devices are stringent requirements for noise resistance of electronic devices against external noise. Moreover, the sources of external noise are ever increasing, and the demand for noise resistance of electronic devices becomes stronger as well as removal of interfering noise, which has been demanded in the past. In particular, on-vehicle electronic devices (on-vehicle intelligent power modules and the like) used in severe environments require stricter anti-noise countermeasures than the conventional level because of the requirements demanded by manufacturers.
Thus, anti-noise countermeasures are taken on a control circuit board for controlling a power semiconductor element or the like, or a shield plate is arranged between the power semiconductor element and the control circuit board. As the former anti-noise countermeasures on the control circuit board side, a metal foil is attached to the entire surface of the control circuit board close to the outer case and is electrically connected to the ground, or circuits or patterns are designed as anti-noise countermeasures, or components for anti-noise countermeasures such as capacitors are provided.
As the latter anti-noise countermeasures of arranging the shield plate, a semiconductor device in which the shield plate is fixed by screwing is known (Patent Literature 1). Moreover, a semiconductor device in which a print board having a shield layer is fixed by screwing to external connection terminals is fixed and supported on an outer case (Patent Literature 2). Moreover, there is a semiconductor device in which a shield plate is mounted on the ends of step supports implanted in an outer case, a metal ring is placed so that a coupling portion of each of the step supports passes through the metal ring, a control circuit board is mounted on the metal rings, the control circuit board and the shield plate overlapped in two stages are fixed by screwing to the step supports (Patent Literature 3). Since these semiconductor devices have the shield plate arranged between the power semiconductor element and the control circuit board, it is possible to suppress noise radiating from one of the power semiconductor element and the control circuit board from entering into the other by being partially blocked by the shield plate. A metal plate made from a material corresponding to the properties of noise is used as the shield plate, and it is possible to effectively block noise.
Patent Literature 1: Japanese Patent No. 4583122
Patent Literature 2: Japanese Patent Application Publication No. 2009-130163
Patent Literature 3: WO 2010/150471
The semiconductor devices disclosed in Patent Literature 1 to 3 use metal screws or metal rings in order to fix the shield plate. Thus, since metal components are used, it is necessary to design by taking a separation distance between the shield plate and the control circuit board mounted above the shield plate into consideration and to prepare a void distance corresponding to a screw height between the shield plate and the control circuit board. Therefore, the overall height of the semiconductor device having the control circuit board increases and the volume increases.